21197857 has 2 divisors, whose sum is σ = 21197858. Its totient is φ = 21197856.

The previous prime is 21197851. The next prime is 21197867. The reversal of 21197857 is 75879112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17648401 + 3549456 = 4201^2 + 1884^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21197857 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21197851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10598928 + 10598929.

It is an arithmetic number, because the mean of its divisors is an integer number (10598929).

Almost surely, 2^21197857 is an apocalyptic number.

It is an amenable number.

21197857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21197857 is an equidigital number, since it uses as much as digits as its factorization.

21197857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 35280, while the sum is 40.

The square root of 21197857 is about 4604.1130524782. The cubic root of 21197857 is about 276.7561748098.

The spelling of 21197857 in words is "twenty-one million, one hundred ninety-seven thousand, eight hundred fifty-seven".